KELLY MCEVERS, HOST:
So there's this bird called the frigatebird. It has a huge wingspan 6-feet wide, and males have these bright red pouches on their throats. The bird spends most of its life at sea, so its habits aren't very well known. But now researchers who've started tracking these birds say their flying abilities almost defy belief. NPR's Christopher Joyce reports on what they found.
CHRISTOPHER JOYCE, BYLINE: To figure out what frigatebirds are doing, biologist Henri Weimerskirch put satellite tags on them. When the data started to come in, he could hardly believe how high the birds flew.
HENRI WEIMERSKIRCH: First, we found, oh, 1,500 meters, whoa, excellent, fantastique. And after 2,000, after 3,000, after 4,000 meters - OK.
JOYCE: 4,000 meters is over 12,000 feet as high as the Rocky Mountains.
WEIMERSKIRCH: There is no other bird that is flying so high relative to the sea surface.
JOYCE: Weimerskirch who's with the National Science Research Center in Paris says that kind of flying should take a huge amount of energy. But his instruments were monitoring the birds' heartbeats, and the birds weren't even winded. How did they do it? Well, they flew into a cloud.
WEIMERSKIRCH: It's the only bird that is known to intentionally enter into a cloud.
JOYCE: A fluffy white cumulus cloud. They form in places where warm air rises from the sea surface. The birds hitch a ride on the updraft. Frigatebirds have to stay up there because they can't land on the water. Their feathers are not waterproof. They steal food from other birds in the air or they fly over a fish-feeding frenzy and scoop up small fish that leap out of the water. So in between meals, frigatebirds soar and soar and soar, in one case for two months continuously aloft.
CURTIS DEUTSCH: Absolutely incredible.
JOYCE: Curtis Deutsch is an oceanographer at the University of Washington.
DEUTSCH: They're doing it right through these cumulus clouds. You know, if you've ever been on an airplane flying through turbulence, you know that it can be a little bit nerve-racking.
JOYCE: The birds were tracked flying over the Indian Ocean. One soared 40 miles without a single wing flap. Several covered 300 miles a day. They can do that because no bird has bigger wings for its body weight. Writing in the journal Science, the researchers discovered that frigatebirds have capitalized on a lucky coincidence. Winds that form these updrafts also disrupt waves at the sea surface. That allows deeper nutrient-rich water to rise which attracts fish, so the birds can just hop off at the bottom of this oceanic rollercoaster, eat and get back on again. Christopher Joyce, NPR News.